1. Field of the Invention
The present invention relates to a 3-dimensional comb structure using an electrostatic force, and an inertia detection sensor and an actuator which uses the 3-dimensional comb structure.
2. Description of the Related Art
A 3-dimensional comb structure using an electrostatic force protrudes perpendicularly with respect to a flat plane surface, and has a structure such that an electrostatic force, which is generated between a pair of interlocked combs by applying a voltage thereto, is constant with respect to the relative motion between the combs.
In many cases, electrostatic actuators are used to move micro structures. An electrostatic comb drive (U.S. Pat. No. 5,025,346) is well known as an electrostatic actuator. The basic principle of the electrostatic comb drive will now be described with reference to FIG. 1.
A pair of combs 1 and 2 mesh with each other with a gap s between fingers thereof. When a power supply 3 is connected to each of the combs 1 and 2 via conductive wires 4 and 5, respectively, a horizontal electrostatic force (F.sub.s) 6 acting upon a finger of the comb 2 is expressed by the following Equation 1: ##EQU1##
wherein .epsilon..sub.0, t, s and V denote the permittivity of free space, the thickness of a finger in a direction perpendicular to the surface, the interval between a finger of the comb 1 and an adjacent finger of the comb 2, and a voltage 3 applied to a bridge between fingers, respectively. The electrostatic comb drive can be manufactured by a CMOS process such as a process for manufacturing a semiconductor RAM, and has a constant force with respect to the motion of a comb, as shown in Equation 1.
FIG. 2 disclosed in U.S. Pat. No. 5,025,346 can be taken as an example of an actuator using the principle of FIG. 1, which is the principle of an existing electrostatic comb drive. This electrostatic actuator 20 includes a mass body 22 having a plurality of movable comb fingers 27, at least one elastic member 23 connected to the mass body 22, and a plurality of fixed combs 25 which are meshed with the movable comb fingers 27, facing the movable comb fingers 27. Here, the plurality of movable comb fingers 27 are supported by a substrate 21 via supporters 24, and the fixed comb fingers 25 are supported by the substrate 21 via fixed comb supporters 26. When a voltage is applied to the fixed comb fingers 25 and the movable comb fingers 27 via an appropriate means (not shown), the mass body 22 is moved linearly in a horizontal direction with respect to the substrate 21 by the electrostatic force generated by Equation 1. The electrostatic force generated in this structure is constant with respect to the distance of motion, as shown in Equation 1. However, according to this structure, the movable comb fingers 27 and the fixed comb fingers 25 are parallel to the substrate 21. Also, since the movable comb fingers 27 and the fixed comb fingers 25 are installed on both ends of the flat mass body which is parallel to the substrate 21, the number of combs can increase in proportion to the length of each end of the mass body. Thus, an electrostatic force is small due to the limit in the number of combs. Furthermore, the mass body must move largely to be used in acceleration sensors or gyro sensors. However, in this conventional comb structure, a small amount of electrostatic force makes it difficult to directly drive the mass body, so that the mass body can only be driven at the resonance point.